JP2692994B2 - Digital protection relay - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention is used in a digital protective relay, particularly in the field of generator protection where error is small over a wide frequency range. The present invention relates to a digital protective relay.

(Prior Art) A protective relay is provided to protect the power system, but in this case, it is often necessary to calculate the amplitude value of the alternating-current electricity quantity of the power system to be protected. At this time, the digital protective relay samples the sine wave current or voltage of the power system or both of them at a predetermined time interval, converts the sampled value into digital data, and uses this digital data to generate a sine wave. The amplitude value of the wave current or voltage is calculated, and the output of the relay is output by comparing the amplitude value and the settling value (predetermined value). 50Hz
Alternatively, as the amplitude value calculation method that can provide good calculation results in the frequency band near the rated system frequency of 60 Hz, the rectification addition method and the binary addition method have already been put into practical use. A few amplitude value calculation methods that can provide good amplitude value calculation results in a wide center frequency band (e.g., 20 Hz to 70 Hz when rated at 50 Hz) have already been proposed.

A conventional amplitude value calculation method for wide frequency band characteristics will be described below with reference to the drawings.

FIG. 6 is a diagram for explaining a conventional amplitude value calculation method having a wide frequency band. In FIG. 6, reference numeral 10 denotes a current data i _m reading processing unit, which reads digital data i _m (m is an integer and indicates a time series) of a sine wave current of a power system for subsequent digital calculation processing. Put in. 11 is a digital filter processing section, to the data i _m of i _m reading process unit 10, a direct current component by (1-z ^-6) / 2 transfer functions, double harmonic, such as 4 times harmonic non Remove the required frequency components. 12
Is a wideband filter processing unit, and in order to realize the wide frequency band characteristic of the amplitude value calculation, frequency components (30 Hz to 70 Hz) other than the vicinity of the rated frequency are (1 + 0.25z ^-6 ) ² /(1-0.2
5) Amplify with a transfer function of ² . The output data I _m of the broadband filter processing unit 12 is input to 13 and is calculated by the square of the amplitude value η ² = ▲ ² _m−3 ▼ −I _m · I _m−6 (1). Reference numeral 14 is a relay determination unit that determines η ² (settled value) ² , and 15 is a trip output unit.

(Problems to be Solved by the Invention) The frequency characteristics of the above-described conventional amplitude value calculation method will be described with reference to the drawings. FIG. 7 is a frequency characteristic diagram of the gain of the conventional amplitude value calculation method. In FIG. 7, the horizontal axis represents the normalized angular frequency ω / ω ₀ normalized by the rated angular frequency ω ₀ , and the vertical axis represents the gain. The following can be seen from FIG. The gain of the conventional amplitude value calculation method is
0.94 to 1.in the normalized angular frequency range of 0.5 to 1.5.
Takes a value between 08. In other words, for the rated frequency of 50 Hz, the amplitude value is calculated with an accuracy of -6 to + 8% in the frequency range of 25 Hz to 75 Hz. As a recent demand for protection of generators, the expansion of protection to low frequency bands such as 10's Hz is becoming stronger. With respect to the extension of protection to such a low frequency range, the conventional amplitude value calculation method has a problem in that the error becomes as high as 50% at 15 Hz.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a digital protective relay to which an amplitude value calculation method applicable to a frequency range higher than that of the related art is applied.

[Configuration of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a system rated frequency
▲ η ² _n ▼ ＝ ▲ I ² _mn for the AC electricity of the power system that is A / D converted after sampling at 4n times the sampling frequency
▼ -I _m · I _m-2n, a plurality of amplitude value calculation processing units, a maximum amplitude detection unit that detects the maximum amplitude value η2 from the plurality of amplitude values ▲ η ² _n ▼, a maximum amplitude value η2 and settling It is composed of a relay judgment unit for comparing the value or its modified value.

 However, n is a natural number and m is an integer indicating a time series.

(Operation) The operation of the above means will be described with reference to the symbols in FIG. The curves of the frequency characteristics of the plurality of amplitude value calculation processing units are respectively the second
They are S1 and S2 in the figure. The frequency characteristic after the processing of the maximum amplitude detecting section 19 is obtained as a curve S that connects the larger curve portions of these two frequency characteristic curves S1 and S2.

(Example) Hereinafter, an example is described with reference to drawings. For convenience of explanation, FIG. 3 will be described. FIG. 3 is an example of a hardware block diagram of the digital protective relay according to the present invention. That is, reference numeral 30 is an input converter which converts each of the input electric quantities X1 to Xn into a voltage of an appropriate magnitude, and an analog filter 31 removes a frequency error from this output. The output of this analog filter is input to the input selection circuit (multiplexer) MPX33 via the sample hold circuit 32 that samples at 4n times the system rated frequency (n is a natural number), and the output selected here is the A / D conversion circuit. It is converted into a digital value at 34 and input to the CPU 35. CPU35 is ROM37 program, R
The calculation is executed based on the data from the AM 38 and the signal from the settling unit 36. If a trip output is required as a result of the operation, the trip output is performed via the interface circuit 39.

FIG. 1 is a software flow chart of the digital protective relay of the present invention. In FIG. 1, the same reference numerals as those in FIG. 6 are used with the same meanings as in FIG. 6, and therefore their explanations are omitted here and only different processing parts will be explained.
However, in FIG. 1, the first digital filter processing unit
11, the first band widening filter processing unit 12 and the first amplitude value calculation processing unit 13 correspond to the digital filter processing unit 11, the band widening filter processing unit 12, and the amplitude value calculation processing unit 13 of FIG. 6, respectively.

In FIG. 1, reference numeral 16 is a second digital filter processing section, 17 is a second wide band filter processing section, 18 is a second amplitude value calculation processing section, and 19 is a maximum amplitude detection section. Second digital filter processing unit 16 receives the output i _m of i _m read processing section ^{10 (1-z -12) /} 2 becomes performs filter processing for removing DC and integral multiples harmonics by the transfer function. The second wideband filter processing unit 17 receives the output of the second digital filter processing unit 16 as an input, and uses a transfer function of {(1 + 0.25z ^-12 ) / (1-0.25)} ² except for near the 1/2 harmonic wave. Frequency component of (1
0 to 40Hz) and frequency components other than near 3/2 harmonic (60 to 80H)
z) is amplified.

The second amplitude value calculation processing unit 18 receives the output J _m of the second broadband filter processing unit 17 as an input, and the following equation (2) ▲ η ² ₂ ▼ = ▲ J ^{2 m-6} ▼ -J _m · J _{m- 12} …… (2) Calculate the square value of the amplitude value. Maximum amplitude detector 19
The output ▲ eta ² ₂ ▼ the output ▲ eta ² ₁ ▼ and second amplitude value calculation processing section 18 of the first amplitude value calculation processing section 13 as an input, the following equation (3)
The square value η ² of the maximum amplitude value is detected by.

η ² = Max {▲ η ² ₁ ▼, ▲ η ² ₂ ▼} (3) However, in the formula (3), Max {▲ η ² ₁ ▼, ▲ η
² ₂ ▼} is an operator that takes the larger of ▲ η ² ₁ ▼ and ▲ η ² ₂ ▼.

FIG. 2 is a frequency characteristic diagram of the gain of the amplitude value calculation method used in the present invention. S (curve indicated by thick line)
Is the curve of total frequency characteristics. In Figure 2, S1
(Curve indicated by chain of black circles) is a curve of the first frequency characteristic that is synthesized by the first digital filter processing unit 11, the first broadband filter processing unit 12, and the first amplitude value calculation processing unit 13. The first frequency characteristic curve S1 corresponds to the amplitude value η ₁ obtained by the equation (1), and is the same as the frequency characteristic curve shown in FIG. 7 of the conventional amplitude value calculation method. In Figure 2, S2
(Curve indicated by chain of white circles) is a curve of the second frequency characteristic which is synthesized by the second digital filter processing unit 16, the second wide band filter processing unit 17, and the second amplitude value calculation processing unit 18. The curve S2 of the second frequency characteristic corresponds to the amplitude value η ₂ obtained by the equation (2), and the curve of the frequency characteristic shown in FIG. 7 of the conventional amplitude value calculation method is the horizontal axis representing the normalized angular frequency. To
It is a curve obtained by reducing to 1/2. The curve S of the total frequency characteristic is the processing η ² = Max {▲ of the maximum amplitude detection unit 19.
As can be seen from η ² ₁ ▼, ▲ η ² ₂ ▼}, it is obtained by connecting the larger curve portions of the first and second frequency characteristic curves S1 and S2. The following can be seen from FIG. The gain of the amplitude value calculation method of the present invention has a normalized angular frequency of 0.25 to 1.
It has a value between 0.94 and 1.08 in the range of 75. In other words, when the rated system frequency is 50 Hz, the frequency is 12.5.
Amplitude values can be calculated with an accuracy of -6 to 8% in the range of Hz to 87.5 Hz.

FIG. 4 is a software flow chart of a digital protection relay according to another embodiment of the present invention. In FIG. 4, the same reference numerals as those in FIG. 1 are used with the same meanings as in FIG. 1, and therefore their explanations are omitted here, and only different processing parts will be explained. 21 is a first digital filter processing unit, 22
Is a first broadband filter processing unit, 23 is a first amplitude value calculation processing unit, 24 is a second digital filter processing unit, 25 is a second broadband filtering process unit, and 26 is a second amplitude value calculation processing unit. The first digital filter processing unit 21, i _m read processing unit
The output i _m of 10 is input, and filtering processing is performed to remove harmonic components of DC and an integral multiple of 1.5 by a transfer function of (1-z ^-8 ) / 2.

The first wideband filter processing unit 22 receives the output of the first digital filter processing unit 21 as an input, and {(1 + 0.21z ^-8 ).
/(1-0.21)} ^{2 is used} to amplify frequency components other than near the rated frequency. First amplitude value calculation processing unit
23, an output I _m of the first wideband filter processing unit 22 as an input, calculates a square value ▲ eta ² ₁ ▼ amplitude value by the following equation (4).

_{^{▲ η 2 1 ▼ = ▲ I}} 2 m-4 ▼ -I m · I m-8 ...... (4) second digital filter processing section 24, i _m read processing unit 10
The output i _{m of} is input, and the filter processing is performed to remove the harmonic component of DC that is an integral multiple of 0.75 by the transfer function of (1-z ^-16 ) / 2. The second broadband filter processing unit 25 receives the output of the second digital filter processing unit 24 as an input, and {(1+
0.21z ^-16 ) / (1-0.21)} ² by the transfer function 1 /
Amplifies frequency components other than the vicinity of the rated frequency of 2. Second
The amplitude value calculation processing unit 26 includes a second wide band filter processing unit 25.
Using the output Jm of as the input, the square value of the amplitude value according to the following equation (5) ▲ η ² ₂ ▼: ▲ η ² ₂ ▼ = ▲ J ² _m-8 ▼ -J _m · J _m-16 (5) To calculate.

FIG. 5 is a frequency characteristic diagram of the gain of the amplitude value calculation method used in the present invention. R (curve indicated by thick line)
Is the curve of total frequency characteristics. R1 in Fig. 5
The curve indicated by the chain of black circles is the combined first frequency characteristic curve of the first digital filter processing unit 21, the first broadband filter processing unit 22, and the first amplitude value calculation processing unit 23. R2 (a curve shown by a chain of white circles) is a curve of the second frequency characteristic that is synthesized by the second digital filter processing unit 24, the second wide band filter processing unit 25, and the second amplitude value calculation processing unit 26. As can be seen from the processing η ² = Max {▲ η ² ₁ ▼, ▲ η ² ₂ ▼} of the maximum amplitude value detection unit 19, the comprehensive frequency characteristic curve R 1 shows the first and second frequency characteristic curves R 1 It is obtained by connecting the larger curve part of and R2. The following can be seen from FIG. The gain of the amplitude value calculation method of the present embodiment of the present invention is in the range of normalized angular frequency 0.25 to 1.25.
It takes a value between 1.0 and 1.05. In other words, in the case of the rated system frequency of 50 Hz, the amplitude value can be calculated with an accuracy of 0 to + 5% in the frequency range of 12.5 Hz to 62.5 Hz.

[Effects of the Invention] As described above, according to the present invention, in the plurality of amplitude value calculation processing units, ▲ η ² _n ▼ = ▲ I ² _mn ▼ -I _m · I _{m-2n with} respect to the AC electric quantity. Calculate the squared value ▲ η ² _n ▼ of multiple amplitude values,
To the square value of the plurality of amplitude values ▲ eta ² _n ▼, calculates the square value eta ² of the maximum amplitude value by the maximum amplitude detection unit, a relay determination to compare the square eta ² and set value of the maximum amplitude value Since this is performed, it is possible to provide a digital protective relay applicable to a wide frequency band including the rated frequency of the system, particularly a wide frequency band on the low frequency side.

[Brief description of the drawings]

FIG. 1 is a software flow chart of an embodiment of a digital protective relay according to the present invention, and FIG. 2 is a gain frequency characteristic diagram of an amplitude value calculation method applied to an embodiment of a digital protective relay according to the present invention. FIG. 4 is a block diagram of hardware of a digital protective relay according to the present invention, FIG. 4 is a flow chart of software according to another embodiment of the present invention, and FIG. 5 is an amplitude value applied to another embodiment of the present invention. Fig. 6 is a gain frequency characteristic diagram of the calculation method, Fig. 6 is a software flow chart of the conventional digital type protective relay, and Fig. 7 is a gain frequency characteristic diagram of the amplitude value calculation method applied to the conventional digital type protective relay. 10 …… i _m Read processing unit 11 …… First digital filter processing unit 12 …… First wide band filter processing unit 13 …… First amplitude value calculation processing unit 14 …… Relay determination unit 15 …… Trip output unit 16 ...... Second digital filter processing unit 17 ...... Second wide band filter processing unit 18 ...... Second amplitude value calculation processing unit 19 ...... Maximum amplitude value detection unit

Claims (1)

(57) [Claims] 1. An alternating current electricity quantity of an electric power system which is A / D converted after sampling at a sampling frequency 4n times the rated frequency of the system, ▲ η ² _n ▼ = ▲ I ² _mn ▼ -I _m · I _{m- 2n,} a plurality of amplitude value calculation processing units, a maximum amplitude detection unit that detects the maximum amplitude value η ² from the plurality of amplitude values ▲ η ² _n ▼, a maximum amplitude value η ² and a settling value or its modified value. A digital protective relay, comprising a relay determination unit for comparison. However, n is a natural number and m is an integer indicating a time series.